Molybdenum carbide catalyst for the reduction of CO to CO: surface science aspects by NAPPES and catalysis studies.

Carbon dioxide is a greenhouse gas, and needs to be converted into one of the useful feedstocks, such as carbon monoxide and methanol. We demonstrate the reduction of CO with H as a reducing agent, via a reverse water gas shift (RWGS) reaction, by using a potential and low cost MoC catalyst. MoC was evaluated for CO hydrogenation at ambient pressure as a function of temperature, and CO : H ratio at a gas hourly space velocity (GHSV) of 20 000 h. It is demonstrated that the MoC catalyst with 1 : 3 ratio of CO : H is highly active (58% CO conversion) and selective (62%) towards CO at 723 K at ambient pressure. Both properties (basicity and redox properties) and high catalytic activity observed with MoC around 700 K correlate well and indicate a strong synergy among them towards CO activation. X-ray diffraction and Raman analysis show that the MoC catalyst remains in the β-MoC form before and after the reaction. The mechanistic aspects of the RWGS reaction were determined by near-ambient pressure X-ray photoelectron spectroscopy (NAPXPS) with in situ generated MoC from carburization of Mo-metal foil. NAPXPS measurements were carried out at near ambient pressure (0.1 mbar) and various temperatures. Throughout the reaction, no significant changes in the Mo oxidation state (of MoC) were observed indicating that the catalyst is highly stable; C and O 1s spectral results indicate the oxycarbide species as an active intermediate for RWGS. A good correlation is observed between catalytic activity from atmospheric pressure reactors and the electronic structure details derived from NAPXPS results, which establishes the structure-activity correlation.